The present invention relates to a process for the preparation of aqueous dispersions of anionic polyurethanes, to the obtained dispersions and to a coated substrate or film obtained with said dispersion.
Aqueous dispersions of polyurethanes are well known as basis for the preparation of coating compositions. They may be used for protective or decorative coating, optionally in combination with additives like coloring agents, pigments, matting agents, and the like. Polyurethanes can posses many desirable properties such as good chemical resistance, water resistance, solvent resistance, toughness, abrasion resistance, durality.
Dispersibility of the polyurethanes in water can be achieved by incorporation of appropriate chain pendant ionic groups, chain pendant non-ionic hydrophilic groups, or in-chain non-ionic hydrophilic groups in the structure of the polyurethane polymer. If suitable, external surfactants can be applied in addition. Preferably anionic groups are incorporated into the polyurethane backbone, such as carboxylic, sulfonic, sulfate or phosphate groups. They are introduced by reaction of a reactive hydrogen functional compound having at least one acid group with a polyisocyanate. Most common is the incorporation of a carboxylic acid functional compound.
The carboxylic acid functions are generally neutralized before or during dispersion of the polyurethane prepolymer into water with a volatile tertiary amine. Anorganic bases are less convenient, since the polyurethane will generally coagulate when they are applied or it will provide highly water sensitive films or coatings. To prevent coagulation it is suitable to incorporate a great number of hydrophilic polyethoxy chains into the polymer system, but the coatings prepared from these dispersions will be very sensitive to water as well.
A disadvantage of the use of volatile tertiary amines as neutralizing agent is that they evaporate during the film formation, and therefore will cause unacceptable environmental pollution.
The present invention offers a process to prepare aqueous dispersions of anionic polyurethanes containing no volatile tertiairy amines.
According to the present invention there is provided a process for the preparation of an aqueous dispersion of an anionic polyurethane in which a tertiary amine functional urethane polymer or oligomer acts as acid neutralising agent. The process according to the present invention comprises the steps of: dispersion of an anionic isocyanate functional polyurethane prepolymer into water in the presence of a tertiary amine functional urethane polymer or oligomer and chain extending the polyurethane prepolymer with a reactive hydrogen functional material during or after the dispersion in water.
The anionic group in the polyurethane to be neutralized may be a carboxylic acid group.
The tertiary amine functional urethane polymer or oligomer of the invention is prepared by the reaction of a polyisocyanate or an isocyanate functional polyurethane prepolymer with a reactive hydrogen functional material which contains tertiary amine functions.
The urethane polymer or oligomer which contains tertiary amine functions can be prepared as a pure oligomeric or polymeric material, it can be prepared in a solvent system, or it can be prepared as an aqueous dispersion. The tertiary amine functional urethane polymer or oligomer of the invention may be prepared by the steps of:
preparation of an isocyanate functional polyurethane prepolymer containing tertiary amine functions from a polyisocyanate, and a polyol which contains tertiary amine functions,
chain extending and/or partially capping of the prepolymer with a reactive hydrogen functional material.
As mentioned above the tertiary amine functional urethane polymer or oligomer may occur in an aqueous dispersion which is prepared by the steps of:
preparation of an isocyanate functional polyurethane prepolymer containing tertiary amine functions from a polyisocyanate, and a polyol which contains tertiary amine functions
dispersion of the prepolymer into water,
chain extending and/or partially capping of the prepolymer with a reactive hydrogen functional material during or after the dispersion into water.
The polyol which contains tertiary amine functions and which is used for the preparation of the polyurethane prepolymer is N-ethyldiethanolamine, N-butyldiethanolamine, N-tert-butyldiethanolamine, 3-diisopropyl-amino-1,2-propanediol, 3-(dimethylamino)-1,2-propanediol, 3-(diethylamino)-1,2-propanediol, triethanol-amine, tripropanolamine, triisopropanolamine and is preferably N-methyldiethanolamine or (3-dimethylamino-propyl)diisopropanolamine.
The reactive hydrogen functional material which is used in the preparation of the tertiary amine functional urethane polymer or oligomer or dispersion thereof is a tertiary amine functional polyol, polyamine, monoamine, monoalcohol or a mixture thereof. When the reactive hydrogen functional material is a polyol or a poly-amine it may be a polyol containing a tertiary amine function as described above or is a diamine which is bis(3-aminopropyl)methylamine.
To obtain a maximal tertiary amine concentration the reactive hydrogen functional material for the capping of the prepolymer is preferably a mono-amine or mono-alcohol containing a tertiary amine function, which may be, 2-(diethylamino)ethylamine, 3-(diethylamino)propyl-amine, N,N,Nxe2x80x2-trimethylethylene-diamine, N,N,Nxe2x80x2-trimethyl-1,3-propane-diamine, N,N,2,2-tetra-methyl-1,3-propane-diamine, N,N-diethylethanolamine, 1-dimethylamino-2-propanol, 3-dimethyl-amino-1-propanol, 2-dimethyl-amino-2-methyl-1-propanol, 1-diethylamino-2-propanol, 3-diethyl-amino-1-propanol, 2-(diisopropylamino)ethanol, 5-diethylamino-2-pentanol, 2-(dibutyl-amino)ethanol and is preferably 2-(dimethylamino)-ethylamine, 3-(dimethyl-amino)propylamine or N,N-dimethyl-ethanolamine or bis(3-dimethylaminopropyl)amine, or mixtures thereof.
The polyisocyanate which is used for the preparation of the tertiary amine functional prepolymer is 2,4-toluene-diisocyanate, 2,6-toluenediisocyanate and mixtures thereof, 1,6-hexanediisocyanate, dicyclohexylmethane-4,4xe2x80x2-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate, or tetramethylxylene-diisocyanate, Nxe2x80x2,Nxe2x80x3,Nxe2x80x2xe2x80x3-tris(6-isocyanato-hexyl)isocyanurate, or N,Nxe2x80x2bis(6-isocya-natohexyl)-N-(6-isocyanatohexylamido)urea, or mixtures thereof.
In order to obtain a fine particle sized dispersion it is suitable to incorporate hydrophilic groups into the tertiary amine functional prepolymer. For this reason other polyols may be present during the prepolymer formation which may be a polyethoxy diol, a poly(ethoxy/-propoxy) diol, a diol containing a pendant ethoxy or (ethoxy/propoxy) chain, a diol containing a carboxylic acid or a sulphonic acid or salt, or mixtures thereof.
The obtained prepolymer may be chain extended or partially capped and partially chain extended. The reactive hydrogen functional reactive material for the chain extending is a diamine which may be; 1,2-diamino-propane, 1,3-diaminopropane, hydrazine, 5-amino-1,3,3-trimethyl-cyclohexanemethyl-amine, methylpentanediamine, hexanediamine, butyldiamine, poly(ethoxy/propoxy)diamine, polyethoxydiamine, polypropoxydiamine, bis(3-amino-propylamine) or a N-hydrazone functional 5-amino-1,3,3-trimethylcyclohexane methylamine, or mixtures thereof.
The anionic polyurethane prepolymer used in the process is prepared by conventional methods. EP 308115 presents an overview of suitable polyols and polyisocyanates as well as of reactive hydrogen functional compounds to chain extend the prepolymer. Essentially the anionic polyurethane of the process contains carboxylic acid groups which are neutralized by the tertiary amine functional urethane polymer or oligomer. The ratio of tertiary amine functions in the neutralizing agent to the carboxylic acid functions in the anionic polyurethane is from 0.5 to 1.5 and prefarably from 0.7 to 1.2.
Both the anionic polyurethane and the tertiary amine functional urethane polymer or oligomer or dispersion thereof may contain additional functional groups with the objective to improve the waterdispersibility, to improve adhesion to substrates at application, for performance reasons, or as potential sites for crosslinking. Suitable functions are polyalkoxy functions with a large concentration of ethoxy functions, are tertiairy amine or quaternairy amine functions, perfluor functions, incorporated silicon functions, hydrazide functions or hydrazone functions, ketone, acetoacetate, or aldehyde functions, or mixtures thereof.
The aqueous polymer dispersions produced by the method of the invention are stable for long periods of time. If desired minor amounts of solvents may be included in the dispersions.
Many additional ingredients may also be present in the application stage, for example fillers, colorants, pigments, silicons, flow agents, foaming agents, matting agents, and the like.
The aqueous polymer dispersions produced by the method of the invention may be used in adhesives, sealants, printing ink and in coatings.
The invention further comprises the dispersions obtained by the process and the coated substrates or films obtained by applying the dispersions onto a substrate such as leather or artificial leather, metals, wood, glass, plastics, paper, paper board, textile, non-woven, cloth, foam and the like by conventional methods, including spraying, flow-coating, transfer-coating, roller coating, brushing, dipping, spreading and the like.
Various aspects features and embodiments of the present invention are illustrated by the following examples. These examples are only illustrative and do not intend to limit the invention as claimed hereafter.